The present invention pertains to secure communications in computer networks and more particularly, to a method and system for performing blinded encryption and decryption in which an encryption agent, decryption agent, or both are denied access to the information being encrypted or decrypted.
The use of encryption in computer networks and particularly the use of public key cryptographic systems such as the well-known RSA algorithm that employ public/private key pairs is well known. In certain circumstances, e.g. systems involving secret recovery, ephemeral decryptability, or enforcement of payment for services, encryption and/or decryption requires the involvement of a third party. Traditional approaches involving decryption by a decryption agent have resulted in the decryption agent having access to the decrypted information. This circumstance requires the decryption agent to be trustworthy. It would be preferable in certain applications to preclude the decryption agent from having access to sensitive information, notwithstanding the decryption agent's participation in the decryption process. Other traditional approaches require authenticating the decryption agent, which is expensive and assumes the existence of a secure public key infrastructure (PKI).
A technology involving blinded signatures is generally related but employed for a different purpose. In the case of a blinded signature, a party (e.g. party B) would like to have some information M signed by party C. Party B, however, does not want party C to be able to access the information M in the document being signed.
To achieve a blinded signature, party B picks a random value R and encrypts R with the RSA public key (e,n) of party C to form an encrypted value. Party B then multiplies the encrypted value by the message M to form a string S=(Re mod n)*M. The string S is communicated to Party C. Party C applies its RSA private key (d,n) to the string S to obtain the string Z=[R]*[Md] mod n. Party C communicates the string Z to party B. B then divides the string Z by the random number R obtain the signed document Md mod n. In the foregoing manner, party B has obtained a copy of the message M signed by Party C without exposing the information M to Party C.
There are several applications in which a decryption agent might aid in decrypting a message. For example, key recovery is a typical application in which the message, which is the secret key, is encrypted with the decryption agent's public key, or a secret key S is used to encrypt the message, and S is encrypted with the decryption agent's public key. If there is no other way to recover the message, for instance because all other copies are lost, then the encrypted message (or the encrypted secret key S) is sent to the decryption agent for decryption. If the decryption agent is not authenticated, it is possible to have a man-in the-middle attack in which an active attacker gets between the client and the decryption agent, and has access to all the data, including the decrypted message, or S if applicable. Another example where a decryption agent is used for decryption is with ephemeral decryption such as disclosed in U.S. Pat. No. 6,363,480 that is assigned to the same assignee as the present application.
It would therefore be desirable to have a system and method that permits an encryption and/or decryption agent to participate in the encryption and decryption process in a manner that does not provide the encryption and/or decryption agent with access to the actual information being encrypted or decrypted.